I have a few more:
- BCN (U2 to LGW, STN and LTN; FR to STN, BA to LCY, LGW and LHR; DY to LGW, ZK to LGW)
- MAD (U2 to LGW and LTN, FR to STN, BA to LHR and LCY, UX to LGW, IB to LHR)
- GVA (U2 to LGW, LTN, STN; BA to LHR, LGW, LCY; LX to LHR, LCY + a bunch of seasonal charters to LGW/STN with Monarch and Thompson)

Quoting eicvd (Reply 1):Do Easyjet fly AMS-SEN? If they do then AMS & DUB have flights to all 6 'London' airports